An aerial 1080 drop over 30,000 hectares in the Northern Ruahine Ranges will take place this Spring to battle an expected surge in predator numbers.

Every 2-6 years beech trees flower and produce massive quantities of seed, in an event known as a 'mast', and sampling by the Department of Conservation in February confirmed a mast was occurring in the Northern Ruahine Ranges this year.​The operation will begin after September 6, as weather permits, and will see cereal baits containing biodegradable sodium fluoroacetate, known as 1080, dropped over 30,000ha.

The targets will be rats, stoats and possums which will be present in much greater numbers due to the short-term bounty of food due to the mast.

DOC's acting operations manager for Manawatu, Duncan Toogood, said the operation had been planned to give maximum protection to the highly valued species in the area.

"This increase in animal pest numbers could lead to the loss of the our threatened taonga species. Once the seed runs out, these predators will look for other food sources—our native species," he said.

The operation will take place over two days. Non-toxic prefeed baits will be dropped over the entire block, at least one week prior to the poison drop. Then poison baits will be aerially sown at 2kg per hectare, at the next available weather window.

After the operation, there will be a withholding period of up to ten months, meaning hunters are advised not to take meat from the area.

DOC is working with OSPRI on the operation and OSPRI will contact all neighbours and place warning signs out immediately prior to the operation starting.

The operation is part of an ongoing battle by DOC to reduce rat, stoat and possum numbers within these ranges.

Without predator control, only 5 per cent of kiwi chicks hatched in the wild will make it to their fourth birthday, and for every three breeding pairs of whio, only two ducklings will make it to fledging.

"Aerial 1080 is the most effective large-scale pest control tool we currently have and monitoring shows it's successful in protecting vulnerable species and allowing birds to produce more chicks to sustain and build their populations," Toogood said.

He said community-led ground-based predator control with more than 1000 traps in the ranges was helping, but trapping could never keep up with the "boom in predator numbers that follows a beech mast, especially over such large-scale, difficult terrain".

The Northern Ruahine operation is one of 34 Battle for our Birds predator control operations taking place across the country this year that together cover about 800,000 ha or 10% of public conservation land.

Battle for our Birds is a nationwide predator control programme that supports DOC's goal of protecting threatened species and making New Zealand predator free by 2050.